Ceramic porous bodies suitable for use with superalloys

ABSTRACT

Ceramic porous bodies, including ceramic foam filters and smooth-faced ceramic objects, e.g., ceramic foam bricks, ceramic foam melting crucibles, and ceramic foam cores, made in accordance with the present invention are suitable for use with molten metal in general and molten superalloys in particular. The invention also provides a tundish for use with ceramic foam filters to filter metal en route from a metal furnace to a casting mold, and a melting device for use in casting metal which employs a ceramic foam filter as a bottom pour valve for a melting crucible such that the ceramic foam filter valve regulates the flow of molten metal therethrough in order to permit an entire ingot of metal to melt in the melting crucible before any metal begins to pour from the melting device into a casting mold.

BACKGROUND OF THE INVENTION

The present invention relates to ceramic porous bodies in general and"ceramic foam filters" in particular. A "ceramic foam filter" is afilter particularly useful in the filtering of molten metal, which ismade by immersing a polyurethane foam pattern into a ceramic slurry,removing excess slurry from the polyurethane foam pattern, and firingthe polyurethane foam pattern to burn away the organic matter andthereby create a porous, hard, self-sustaining ceramic article.

Ceramic foam filters have been known for at least about twenty years.They were described almost simultaneously in U.S. Pat. Nos. 3,090,094(Schwartzwalder et al.), 3,097,930 (Holland), and 3,111,396 (Ball).Since then a number of companies have worked to develop ceramic foamfilters for use in the filtering of aluminum, copper, and other metalshaving a melting point of less than 1200° C. Companies doing work inthis field have included Swiss Aluminium Limited of Switzerland (U.S.Pat. Nos. 3,893,917, 3,947,363, 3,962,081, 4,024,056, and 4,081,371) andthe Bridgestone Tire Company Limited of Japan (U.S. Pat. Nos. 4,257,810and 4,258,099). Heretofore, however, there has not been available aceramic foam filter which is suitable for use with superalloys, i.e.,metals having melting points in excess of 1200° C. In fact, prior to thedevelopment of the present invention several attempts were made to usepresently available ceramic foam filters with superalloys but theseefforts were unsuccessful.

SUMMARY OF THE INVENTION

It is, therefore, a main object of the present invention to provideceramic porous bodies in general and ceramic foam filters in particularwhich overcome the above-mentioned drawback.

It is a more specific object of the present invention to provide ceramicporous bodies in general and ceramic foam filters in particular whichare suitable for use with superalloys.

A further object of this invention is to provide ceramic porous bodiesin general and ceramic foam filters in particular which are superior toprior art ceramic objects in general and ceramic foam filters inparticular used with metals having melting points below 1200° C., suchas aluminum and copper.

Another object of this invention is to provide a tundish particularlysuitable for use with a ceramic foam filter in the filtering of moltenmetal en route from an alloy furnace to an ingot mold.

An additional object of this invention is to provide a process forsimultaneously filtering and casting molten metal.

A still further object of this invention is to provide a melting devicefor use in air or vacuum melting of an ingot of metal which utilizes aceramic foam filter valve to permit an entire ingot of metal to meltbefore any metal is poured from the melting device.

An additional object of this invention is to provide ceramic porousbodies having one or more solid, high density, high purity, smooth facesfor use as: insulating refractory linings for furnaces, kilns andladles; melting crucibles; ceramic cores; and other similar objects.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of instrumentalities and combinations particularly pointed out inthe appended claims.

To achieve the objects, and in accordance with the purpose of theinvention, as embodied and broadly described herein, the inventioncomprises a process for making a ceramic porous body suitable for usewith molten metals in general and molten superalloys in particular whichcomprises the steps of: providing an open-cell, flexible foam pattern;impregnating the foam pattern with a ceramic slurry; burning out thefoam pattern at a temperature of between 1400° F. and 2200° F. to form aceramic substrate; impregnating the ceramic substrate with additionalceramic slurry; and firing the impregnated ceramic substrate at atemperature of between 2200° F. and 3400° F.

To further achieve the objects, and in accordance with the purpose ofthe invention, as embodied and broadly described herein, the inventioncomprises a ceramic porous body suitable for use with molten metals ingeneral and molten superalloys in particular made by the process whichcomprises the steps of: providing an open-cell, flexible foam pattern;impregnating the foam pattern with a ceramic slurry; burning out thefoam pattern at a temperature of between 1400° F. and 2200° F. to form aceramic substrate; impregnating the ceramic substrate with additionalceramic slurry; and firing the impregnated ceramic substrate at atemperature of between 2200° F. and 3400° F.

To further achieve the objects, and in accordance with the purpose ofthe invention, as embodied and broadly described herein, the inventioncomprises a ceramic foam filter useful for filtering molten metals ingeneral and molten superalloys in particular made by the process whichcomprises the steps of: providing an open-cell, flexible foam pattern;impregnating the foam pattern with a ceramic slurry; burning out thefoam pattern at a temperature of between 1400° F. and 2200° F. to form aceramic substrate; impregnating the ceramic substrate with additionalceramic slurry; and firing the impregnated ceramic substrate at atemperature of between 2200° F. and 3400° F.

To further achieve the objects in accordance with the purpose of theinvention, as embodied and broadly described herein, the inventioncomprises a method of filtering molten metals in general and moltensuperalloys in particular, which comprises the steps of: providing aceramic foam filter; positioning the ceramic foam filter so that moltenmetal will pass through the ceramic foam filter when the molten metal ispoured; and pouring the molten metal through the ceramic foam filter;wherein the ceramic foam filter is made by the process which comprisesthe steps of: impregnating an open-cell, flexible foam pattern with aceramic slurry; burning out the foam pattern at a temperature of between1400° F. and 2200° F. to form a ceramic substrate; impregnating theceramic substrate with additional ceramic slurry; and firing theimpregnating ceramic substrate at a temperature of between 2200° F. and3400° F.

To further achieve the objects in accordance with the purpose of theinvention, as embodied and broadly described herein, the inventioncomprises a tundish, for use with a ceramic foam filter to filter moltenmetal, comprising a monolithic body having a bottom pour draining outletand means for maintaining a ceramic foam filter in the path of moltenmetal passing through said tundish to said draining outlet.

To further achieve the objects in accordance with the purpose of theinvention as embodied and broadly described herein, the inventioncomprises a melting device for use in air or vacuum melting of an ingotof metal, the device comprising a monolithic crucible having a bottompore outlet and a ceramic foam filter valve adapted to be fitted intothe bottom pore outlet; the length, the thickness, the diameter, theceramic composition, and the pore size of the ceramic foam filter valvebeing selected to control the flow of metal through the ceramic foamfilter valve such that in operation an entire ingot of metal may beallowed to melt in the crucible before any metal begins pouring from themelting device.

To further achieve the objects in accordance with the purpose of theinvention, as embodied and broadly described herein, the inventioncomprises a process for making a ceramic porous body suitable for usewith molten metals in general and molten superalloys in particularhaving a solid, high density, high purity, smooth face which comprisesthe steps of: providing an open-cell, flexible, foam pattern, and a facepattern the size and shape of a face of the foam pattern to be smoothed;coating the face pattern with a ceramic slurry; stuccoing the facepattern with a coarse ceramic material; impregnating the foam patternwith the ceramic slurry; placing the impregnated foam pattern on thecoated, stuccoed face pattern such that the impregnated foam pattern andthe coated, stuccoed face pattern dry together and become attached;impregnating the attached impregnated foam pattern and coated, stuccoedface pattern with additional ceramic slurry; removing excess driedceramic down to the edges of the foam pattern; burning out the foampattern and the face pattern at a temperature of between 1400° F. and2200° F. to form a ceramic substrate; impregnating the ceramic substratewith additional ceramic slurry; and firing the impregnated ceramicsubstrate at a temperature of between 2200° F. and 3400° F.

The foregoing and other objects, features, and advantages of the presentinvention will be made more apparent from the following description ofthe preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a preferred embodiment of theprocess of making ceramic porous bodies of the present invention.

FIG. 2 is a cross-sectional view of a standard viscosity measuring cupused to obtain the values for viscosity reported herein. The dimensionsof the viscosity measuring cup are identified.

FIG. 3 is a perspective view of apparatus used to obtain the values forceramic slurry film weight reported herein.

FIG. 4 is a schematic block diagram illustrating another embodiment ofthe process of making ceramic porous bodies of the present invention.

FIG. 5 is a diagram illustrating the selection of ingots from a pouredheat to obtain beginning, middle, and end of pour samples.

FIG. 6 is a graphic illustration of average zyglo ratings for thebeginning, middle and end of pour locations of two heats of nickel-basesuperalloy poured through ceramic foam filters of the present invention.

FIG. 7 is a graphic illustration of the frequency distribution of zygloratings for castings made from heats of alloys poured through ceramicfoam filters of the present invention, castings made from heats ofunfiltered alloys, and castings made from heats of alloys poured throughcommercially available filters.

FIG. 8 is a graphic illustration of the overall average zyglo ratingsfor each heat of alloys poured through ceramic foam filters of thepresent invention, unfiltered alloys, and alloys poured throughcommercially available filters.

FIG. 9 is a graphic illustration of the percentage of castings notrequiring reworking for each heat of alloys poured through ceramic foamfilters of the present invention, unfiltered alloys, and alloys pouredthrough commercially available filters.

FIG. 10 is a perspective view in partial cut-away of an embodiment ofthe method of filtering molten metal of the present invention.

FIG. 11 is a perspective view in partial cut-away of an embodiment ofthe tundish of the present invention.

FIG. 12 is a perspective view in partial cut-away of another embodimentof the tundish of the present invention.

FIG. 13 is a perspective view in partial cut-away of another embodimentof a method of filtering metal of the present invention.

FIG. 14 is a photograph of a ceramic foam filter of the presentinvention in the pouring cup of a casting mold before casting an alloyin accordance with an embodiment of the method of filtering molten metalof the present invention.

FIG. 15 is a photograph of a ceramic foam filter of the presentinvention in the pouring cup of a casting mold after casting an alloy inaccordance with an embodiment of the method of filtering molten metal ofthe present invention.

FIG. 16 is a cross-sectional view of an embodiment of a melting deviceof the present invention being used in a method of filtering moltenmetal in accordance with the present invention.

FIG. 17 is a cross-sectional view of another embodiment of a meltingdevice of the present invention being used in a method of filteringmolten metal in accordance with the present invention.

FIG. 18 is a cross-sectional view of another embodiment of a meltingdevice of the present invention being used in a method of filteringmolten metal in accordance with the present invention.

FIG. 19 is another cross-sectional view of the FIG. 18 embodiment of themelting device of the present invention depicting the filtering ofmolten metal in accordance with the present invention.

FIG. 20 is a photograph of two ceramic foam filters of the presentinvention.

FIG. 21 is a schematic block diagram illustrating an embodiment of theprocess of making a smooth faced ceramic porous body of the presentinvention.

FIG. 22 is a photograph of a ceramic foam brick of the presentinvention.

FIG. 23 is an exploded perspective view of a ceramic foam brick of thepresent invention being used as an insulating refractory lining for aladle in accordance with the present invention.

FIG. 24 is a photograph of an embodiment of a ceramic foam meltingcrucible of the present invention.

FIG. 25 is a perspective view of another embodiment of a ceramic foammelting crucible of the present invention.

FIG. 26 is a perspective view of a ceramic foam core of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention.

The process for making a ceramic porous body suitable for use withmolten metals in general and molten superalloys in particular inaccordance with the present invention comprises the steps of: providingan open-cell, flexible, foam pattern; impregnating the foam pattern witha ceramic slurry; burning out the foam pattern at a temperature ofbetween 1400° F. and 2200° F. to form a ceramic substrate; impregnatingthe ceramic substrate with additional ceramic slurry; and firing theimpregnated ceramic substrate at a temperature of between 2200° F. and3400° F.

For purposes of the present invention a "flash" type burn-out of thefoam at a temperature of between 1400° F. and 2200° F., preferably atabout 1800° F., is used to safeguard against fracture of the foamstructure that may result if lower temperature foam removal were used.The temperature at which the impregnated ceramic substrate is fired maybe between 2200° F. and 3400° F., and is preferably about 3100° F.Burning out the foam pattern and firing the ceramic substrate in thismanner greatly strengthens the resulting product.

For purposes of the present invention a wide variety of open-cellflexible foam pattern materials may be used. Suitable materials includepolyurethane, polyethylene, polypropylene and graphite. Good resultshave been obtained with a reticulated, fully open pore, flexible, estertype polyurethane foam material in sizes ranging from 10 to 30 pores perinch.

The ceramic slurry used in accordance with the present invention mayvary. Either a single slurry system or a multiple slurry system may beused for the impregnation steps. In either case best results areachieved when the slurry composition and specifications are controlledto obtain optimal slurry impregnation.

FIG. 1 illustrates a preferred embodiment of the present inventionwherein a single slurry system is used for all of the impregnationsteps. As embodied herein, a polyurethane foam pattern is first filledwith ceramic slurry by dipping the pattern into a ceramic slurrydipcoat. Excess slurry is then displaced from the pattern by squeezing.Compressing the pattern several times by hand is a suitable means fordisplacing the excess slurry. Other squeezing techniques would also besuitable for this step. Next the pattern is dried. Room temperaturedrying for a period of between 4 to 6 hours should be sufficient. Thepattern is then redipped into the ceramic slurry dipcoat. Excess slurryis then displaced from the pattern without squeezing. Preferably, thepattern is allowed to drain in an air stream which serves to breakdownthe occasional webs which form between cell walls. Thereafter thepattern is again dried. Room temperature drying for a period of from 4to 6 hours is suitable here as well. The redipping, draining, and dryingstep may be repeated. Preferably, these steps are repeated at leastonce. After the last series of redipping, draining, and drying steps thepattern is allowed to dry preferably at room temperature for 24 hours.After drying, the sides of the pattern may be smoothed with 180 meshsand paper if desired. Next, the polyurethane foam is burned out at atemperature of between 1400° F. and 2200° F., preferably 1800° F. Thismay be done by placing the pattern directly on a burn-out tray andholding it in a burn-out furnace for 2 or more hours. After burn-out,the resulting ceramic substrate is cooled preferably to room temperatureand then dipped into the ceramic slurry dipcoat again. Excess slurry isthen drained from the ceramic substrate preferably by use of an airstream to break down any webs which may have formed between cell walls.The ceramic substrate is then allowed to dry. Drying at room temperaturefrom 4 to 6 hours should be sufficient. Finally, the ceramic substrateis fired at a temperature of between 2200° F. and 3400° F., preferably3100° F. Good results have been achieved by firing in a zirconiacrucible kiln.

For purposes of this invention the ceramic slurry dipcoat used in theembodiment illustrated in FIG. 1 may have a composition of between 1%and 20% silica by weight (dry basis) and between 99% and 80% alumina byweight (dry basis), a viscosity of between 5 and 20 seconds, and a filmweight of between 1.0 and 8.0 grams per standard six inch square plate.

The values for viscosity reported herein are those which are obtained bymeasuring the time it takes a ceramic slurry to pass through a viscositycup having the dimensions of the standard viscosity cup illustrated inFIG. 2.

Apparatus for determining a slurry's film weight per standard 6 inchsquare plate is shown in FIG. 3. The apparatus includes: a 6 inch squareby 1/16th inch thick brass plate (1) having a dipping line (2) and adrain boss (3) having a 3/4 inch by 3/32 inch diameter, and a platestand (4) on which the brass plate may be mounted. To measure a ceramicslurry's film weight the following procedure is followed: the plate andstand are weighed; the plate is then dipped into the slurry to bemeasured up to the dipping line, then placed on the plate stand andallowed to drain until dripping stops (3-4 minutes); and then the wetplate and stand are weighed. The difference between the wet weight andthe dry weight equals the film weight of the slurry. The brass platesused in this procedure need to be checked periodically against an unusedmaster, since excessive scratching of the surface will result in toohigh a weight of retained slurry.

For purposes of this invention, the ceramic slurry dipcoat compositionmay also include a suspending agent, a wetting agent, and a defoamingagent. Good results have been obtained when polyvinyl chloride latex wasused as a suspending agent, VICTAWET, an organic phosphate ester wasused as a wetting agent, and ethylhexanol was used as a defoaming agent.

VICTAWET is an organic phosphate ester trademarked wetting agentsupplied by the Industrial Chemicals Division of Stauffer ChemicalCompany. The chemical and physical properties of VICTAWET are listed inTable 1.

                  TABLE 1                                                         ______________________________________                                        Chemical:                                                                     P.sub.2 O.sub.5 weight percent - 16 min.                                      Acid #0.1 maximum as mg KOH/g sample                                          Physical:                                                                     Appearance      Liquid with no more than slight                                               haze. Distinctive odor.                                       Color APHA Standard                                                                           500 max.                                                      pH 0.5% solution in                                                                            7.0-7.4                                                      water                                                                         Specific Gravity                                                                              1.110-1.123                                                   Surface tension 0.2%                                                                          29.4 dynes cm.sup.2                                           at room temperature                                                           Draves test at 0.2%                                                                           12 seconds                                                    conc.                                                                         ______________________________________                                    

For purposes of the present invention, the ceramic slurry dipcoat usedin the single slurry system embodiment illustrated in FIG. 1 preferablycomprises about 9.2 silica by weight (dry basis) and about 90.8% aluminaby weight (dry basis), has a viscosity of between 10 and 13 seconds, anda film weight of between 3.7 and 4.0 grams per standard six inch squareplate. A suitable source of silica is aqueous colloidal silica and asuitable source of alumina is -325 mesh alumina flour. Table 2 setsforth the slurry composition and specifications of an example of such aceramic slurry dipcoat with which good results have been obtained.

                  TABLE 2                                                         ______________________________________                                        Slurry Composition:                                                           Aqueous Colloidal Silica                                                                          12,800      ml                                            Latex (polyvinyl chloride)                                                                        740         ml                                            Ethylhexanol        100         ml                                            VICTAWET            400         ml                                            T-61 (-325 m) Alumina Flour                                                                       100         lb                                            Distilled Water     As required                                                                   to adjust                                                                     film weight                                                                   to 3.7-4.0 g                                              Mix in above order.                                                           Specifications:                                                               Viscosity  =          10-13 sec.                                              Film Wt.   =         3.7-4.0 g. per 6 in. sq. plate                           Temperature                                                                              =          68-75° F.                                        pH         =         8.0-9.5                                                  % SiO.sub.2                                                                              =          9.2 (Dry Wt. Basis)                                     % Al.sub.2 O.sub.3                                                                       =         90.8 (Dry Wt. Basis)                                     ______________________________________                                    

FIG. 4 illustrates a second embodiment of the present invention. In thisembodiment, two different ceramic slurries are used, a ceramic slurryprewet and a ceramic slurry dipcoat. In this second embodiment, the stepof impregnating the foam pattern with ceramic slurry is accomplished bydipping the pattern into prewet, draining the pattern by squeezing,dipping the pattern into dipcoat, draining the pattern by squeezing,drying the pattern, redipping the pattern into prewet, draining thepattern without squeezing, redipping the pattern into dipcoat, drainingthe pattern without squeezing and drying the pattern. The redipping intoprewet, draining without squeezing, redipping into dipcoat, drainingwithout squeezing and drying sequence may be repeated, and preferably isrepeated at least once. As for the step of impregnating the ceramicsubstrate with additional ceramic slurry after the burn-out, this isaccomplished by dipping the substrate into the pre-wet, draining thesubstrate, and then drying the substrate. In a variation of thisembodiment the prewet alone without the dipcoat is used for the veryfirst dip of the foam pattern. As in the first embodiment, preferably anair stream is employed during draining to break down any webs which mayhave formed between cell walls.

For purposes of the present invention, the ceramic slurry prewet used inthe FIG. 4 embodiment may have a composition of between 1% and 30%silica by weight (dry basis), and between 99% and 70% alumina by weight(dry basis), and a viscosity of between 1 and 25 seconds, and theceramic slurry dipcoat may have a composition of between 1% and 20%silica by weight (dry basis) and between 99% and 80% alumina by weight(dry basis), a viscosity of between 5 and 60 seconds, and a film weightof between 1.0 and 8.0 grams per standard six inch square plate.Preferably, the ceramic slurry prewet comprises about 11.9% silica byweight (dry basis) and about 88.1% alumina by weight (dry basis) and hasa viscosity of between 8 and 10 seconds, and the ceramic slurry dipcoatcomprises about 9.2% silica by weight (dry basis) and about 90.8%alumina by weight (dry basis), has a viscosity of between 24 and 30seconds, and a film weight of between 4.5 and 5.5 grams per standard sixinch square plate. A suitable source of silica is aqueous colloidalsilica and a suitable source of alumina is -325 mesh alumina flour. Boththe ceramic slurry prewet and the ceramic slurry dipcoat may alsoinclude a suspending agent, a wetting agent, and a defoaming agent.Preferably, the suspending agent is polyvinyl chloride latex, thewetting agent is VICTAWET, and the defoaming agent is ethylhexanol.Table 3 sets forth the composition and specifications for an example ofsuch a ceramic slurry prewet and a ceramic slurry dipcoat suitable foruse in the FIG. 4 embodiment of the present invention.

                  TABLE 3                                                         ______________________________________                                        Prewet:                                                                       Composition:                                                                  Aqueous Colloidal Silica                                                                           17,066     ml                                            Latex (polyvinyl chloride)                                                                         987        ml                                            Ethylhexanol         130        ml                                            VICTAWET             130        ml                                            T-61 Alumina Flour (-325 M)                                                                        100        lb                                            Mix in above order.                                                           Specifications:                                                               Viscosity, seconds     8-10                                                   % Al.sub.2 O.sub.3 = 88.1 (Dry Wt. Basis)                                     % SiO.sub.2 = 11.9 (Dry Wt. Basis)                                            Dipcoat:                                                                      Composition:                                                                  Aqueous Colloidal Silica                                                                           12,800     ml                                            Latex                740        ml                                            Ethylhexanol         100        ml                                            VICTAWET             400        ml                                            T-61 Alumina Flour (-325 M)                                                                        100        lb                                            Mix in above order.                                                           Specifications:                                                               Viscosity, seconds    24-30                                                   Film Wt., g. per 6 in. sq. plate                                                                    4.5-5.5                                                 Temperature °F.                                                                              68-75                                                   pH                    8.0-9.5                                                 % Al.sub.2 O.sub.3 = 90.8 (Dry Wt. Basis)                                     % SiO.sub.2 = 9.2 (Dry Wt. Basis)                                             ______________________________________                                    

Alternatively, for purposes of the present invention the ceramic slurryprewet used in the FIG. 4 embodiment may have a composition of between1% and 30% colloidal silica solids by weight (dry basis) and between 99%and 70% fused silica solids by weight (dry basis), and a viscosity ofbetween 1 and 25 seconds; and the ceramic slurry dipcoat may have acomposition of between 1% and 20% colloidal silica solids by weight (drybasis) and between 99% and 80% fused silica solids by weight (drybasis), a viscosity of between 10 and 80 seconds, and a film weightbetween 1 and 14 grams per standard six inch square plate. Preferably,such a ceramic slurry prewet comprises about 24.8% colloidal silicasolids by weight (dry basis) and about 75.2% fused silica solids byweight (dry basis), and has a viscosity of between 6 and 8 seconds; andsuch a ceramic slurry dipcoat comprises about 12.4% colloidal silicasolids by weight (dry basis) and about 87.6% fused silica solids byweight (dry basis), has a viscosity of between 40 and 50 seconds, and afilm weight between 5 and 7 grams per standard six inch square plate. Asuitable source of fused silica solids is -325 mesh fused silica flour.Both the ceramic slurry prewet and the ceramic slurry dipcoat may alsoinclude a suspending agent, a wetting agent, and a defoaming agent.Preferably, the suspending agent is polyvinyl chloride latex, thewetting agent is VICTAWET, and the defoaming agent is ethylhexanol.Table 4 sets forth the composition and specifications for an example ofsuch a ceramic slurry dipcoat and ceramic slurry prewet suitable for usein the FIG. 4 embodiment of the present invention.

                  TABLE 4                                                         ______________________________________                                        Composition:                                                                  ______________________________________                                        Dipcoat                                                                       Aqueous Colloidal Silica                                                                            12,800     ml                                           Latex                 740        ml                                           Ethylhexanol          100        ml                                           VICTAWET              560        ml                                           -325 Fused Silica Flour                                                                             72         lb                                           Prewet                                                                        Aqueous Colloidal Silica                                                                            12,800     ml                                           Latex                 740        ml                                           Ethylhexanol          100        ml                                           VICTAWET              460        ml                                           -325 Fused Silica Flour                                                                             36         lb                                           Specifications (Dipcoat)                                                      Viscosity = 40-50 sec.                                                        Film Wt. = 5-7 g. per 6 in. sq. plate                                         24.8% Colloidal SiO.sub.2 Solids                                              75.2% Fused SiO.sub.2 Solids                                                   100% SiO.sub.2 (Amorphous)                                                   Specification (Prewet)                                                        Viscosity = 6-8 Sec.                                                          12.4% Colloidal SiO.sub.2 Solids                                              87.6% Fused SiO.sub.2 Solids                                                   100% SiO.sub.2 (Amorphous)                                                   ______________________________________                                    

In accordance with the present invention, both the FIG. 1 and FIG. 4embodiments thereof may be modified by using a special post-burn-outceramic slurry for the dipping of the ceramic substrate after the burnout step. For purposes of the present invention this post-burn-outceramic slurry may comprise zirconia and have a viscosity of between 1and 20 seconds, preferably 5 seconds. A suitable source of zirconia is-325 mesh zirconia. Alternatively, the post-burn-out ceramic slurry maycomprise alumina and have a viscosity of between 1 and 20 seconds,preferably 7 seconds. A suitable source of alumina is A-17 gradecalcined alumina. For both the zirconia post-burn-out ceramic slurry andthe alumina post-burn-out ceramic slurry it is preferable to alsoinclude a polyelectrolyte dispersing agent and a suspending agent. Apreferred polyelectrolyte dispersing agent is DARVAN 7 and a preferredsuspending agent is citric acid. DARVAN 7 is a trademarkedpolyelectrolyte dispersing agent supplied by the Specialties Departmentof R. T. Vanderbilt Company, Inc. Table 5 sets forth the specificationsfor DARVAN 7.

TABLE 5

Chemical Composition: A polyelectrolyte dispersing agent in aqueoussolution.

Physical Form: Clear to slightly opalescent liquid.

Color: Water white.

Total Solids: 25±1%

Specific Gravity: 1.16±0.02.

pH: 9.5-10.5.

Viscosity: 75 cps maximum.

For purposes of the present invention the composition and compounding ofan example of a zirconia post-burn-out ceramic slurry suitable for usein either the FIG. 1 or FIG. 4 embodiments of the present invention areset forth in Table 6 and the composition and compounding of an exampleof a alumina post-burn-out ceramic slurry (which contains A-17 GRADECALCINED ALUMINA which has an ultimate crystal size between 3.0 and 3.5μm and an aluminum content greater than 99.5%) suitable for use ineither the FIG. 1 or FIG. 4 embodiment of the present invention are setforth in Table 7.

                  TABLE 6                                                         ______________________________________                                        100% Stabilized Zirconia Post-Burn-Out                                        Ceramic Slurry                                                                ______________________________________                                        Composition:                                                                  -325 Zirconia   3000 g                                                        DARVAN 7        9 g                                                           Distilled Water 600 g                                                         Citric Acid     3 g                                                           Compounding:                                                                  Ball Mill 24 hours. If thixotropic add                                        more citric acid and mill longer. Transfer                                    to storage container and adjust viscosity to                                  five (5) seconds prior to use.                                                ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        100% Alumina Post-Burn-Out                                                    Ceramic Slurry                                                                ______________________________________                                        Composition:                                                                  A-17 grade Calcined Alumina                                                                        2000 g                                                   Distilled H.sub.2 O  320 g                                                    DARVAN 7             2 g                                                      Citric Acid          1 g                                                      Compounding:                                                                  Ball Mill 24 hours, transfer to storage                                       container and adjust viscosity to seven                                       (7) seconds prior to use.                                                     ______________________________________                                    

Ceramic foam filters and other ceramic porous bodies made by theabove-described embodiments of the present invention are suitable foruse with molten metals in general and molten superalloys in particular,thus overcoming the disadvantages associated with prior art ceramic foamfilter which were not suitable for use with molten superalloys. Thesuitability of ceramic foam filters and other ceramic porous bodies ofthe present invention for use with superalloys is illustrated by thetesting described in Example 1.

EXAMPLE 1

In order to determine whether or not the ceramic foam filter of thepresent invention was deteriorating during the later part of a pour,tests were run to determine if any significant differences in zygloquality existed between the beginning, middle, and end of filteredheats. Two heats of a nickel-base superalloy were poured without filtersand two heats of a nickel-base superalloy were poured through ceramicfoam filters made by the process illustrated in FIG. 4 using the ceramicslurry prewet and dipcoat described in Table 3. For the last three heatsthat were poured (2d unfiltered and both filtered), backfilling of theingots was intentionally started earlier during the pour and the tappingblock drained into two ingot tube molds. After completion of each pour,thirty ingots were color coated; ten each from the beginning, middle,and end of the pour. From original beginning of pour ingots, three wereselected. From the ten middle of pour ingots, four were selected andfrom the end pour ingots, three were selected. This gave a total of ten16 pound charges for each heat (see FIG. 5). The charges were visuallyinspected and spot hand ground as deemed necessary. The charges werethen cast into parts. Each part was assigned a zyglo rating from 1 to 5,number 5 being the best rating. The zyglo results for the beginning,middle, and end of pour locations for the various heats are shown inFIG. 6. This data reveals that the end of pour ingots received improvedzyglo results in comparison to the beginning or middle of pourlocations. In view of the fact that there is an improvement in thequality at the end of the heat, it would seem logical to assume that thefilter is not significantly deteriorating throughout the pour. (Itshould be noted that from historical data from controlled statisticalexperiments end of pour zyglo results tend to be better than thebeginning or middle of pour heats with certain furnaces.)

Testing of two heats of a nickel-base superalloy filtered withcommercially available filters conducted simultaneously and by the samemethod as was used in the above-described testing showed that zygloratings of castings made from metal poured through ceramic foam filtersof the present invention were superior to zyglo ratings of castings madefrom either the unfiltered metal or the metal filtered throughcommercially available filters. A frequency distribution showing theindividual zyglo ratings for each heat is shown in FIG. 7. The two heatsfiltered with the ceramic foam filter of the present invention show anarrower distribution in comparison to either the heats filtered withcommercially available filters or the unfiltered heats. The overallaverage zyglo ratings for each heat is shown in FIG. 8. The heatsfiltered through ceramic foam filters of the present invention receivedthe superior zyglo ratings, followed by one or the heats filteredthrough the commercially available filter. Next in line were the twounfiltered heats and lastly the remaining heat filtered through thecommercially available filter.

After the castings were sent through normal production cycles and thefinal zyglo operation, they were classified as either rework or good.FIG. 9 shows the percentage of castings which did not require reworking.As can be seen, the castings made from metal poured through filters ofthe present invention had the highest percentage of castings which didnot need reworking.

Final analysis of each of the heats tested is given in Table 8. Heats140B11135 and 140B11136 were unfiltered. Heats 140B11137 and 140B11138were poured through ceramic foam filters of the present invention (FIG.4 embodiment; Table 3 prewet and dipcoat composition). Heats 27E6294 and27E6280 were poured through commercially available filters.

                                      TABLE 8                                     __________________________________________________________________________    Element                                                                            140B11135                                                                           140B11136                                                                           140B11137                                                                           140B11138                                                                           27E6294                                                                            27E6280                                     __________________________________________________________________________    C    .09   .081  .09   .09   .086 .080                                        Si   .02   .03   .03   .02   .04  .02                                         Mn   .01   .01   .01   .01   .01  .01                                         Co   9.22  9.16  9.16  9.22  9.00 9.01                                        Ni   Bal   Bal   Bal   Bal   Bal  Bal                                         Cr   12.41 12.52 12.56 12.43 12.71                                                                              12.64                                       Fe   .10   .08   .06   .09   .06  .06                                         Mo   1.84  1.87  1.87  1.88  1.92 1.82                                        W    4.10  4.13  4.11  4.11  4.25 4.21                                        P    .001  .002  .002  .003  .002 .002                                        Ti   3.97  4.00  3.97  4.03  3.94 4.00                                        Al   3.60  3.46  3.42  3.55  3.32 3.50                                        Nb   .02   .02   .03   .03   .01  .01                                         Ta   4.11  4.08  4.04  4.07  4.09 4.10                                        V    .02   .02   .02   .02   .01  .01                                         B    0.14  .014  .016  .014  .013 .014                                        S    .001  .003  .003  .003  .001 .001                                        Zr   .049  .048  .047  .05   .047 .044                                        Cu   .01   .03   .02   .03   .01  .02                                         Hf   .82   .85   .84   .85   .72  .80                                         Pb(ppm)                                                                            <.1   <.1   .1    <.1   .2   .2                                          Bi(ppm)                                                                            <.1   <.1   <.1   <.1   <.1  <.1                                         Ag(ppm)                                                                            <.1   <.1   <.1   <.1   <.1  <.1                                         Se(ppm)                                                                            <.5   <.5   <.5   <.5   <.5  <.5                                         Te(ppm)                                                                            <.1   <.1   <.1   <.1   <.1  <.1                                         Tl(ppm)                                                                            <.1   <.1   <.1   <.1   <.1  <.1                                         Mg(ppm)                                                                            18/21 36/26 27/26 30/27 18   23                                          N(ppm)                                                                             9     7     5     9     8    18                                          O(ppm)                                                                             4     2     4     4     4    2                                           Nv   2.39  2.37  2.27  2.39  2.33 2.38                                        __________________________________________________________________________

The ceramic foam filters of the present invention may be used infiltering a wide range of metals. Table 9 contains a list of superalloyswhich have been successfully filtered with ceramic foam filters of thepresent invention.

                  TABLE 9                                                         ______________________________________                                        Alloy           "V" Number                                                    ______________________________________                                        Nickel Base - Pour Temperature 2700° F./2750° F.                Hastelloy B     150                                                           U-700            85                                                           Mar-M-200 + Hf  132                                                           IN-738LC        141                                                           IN-713C          91                                                           IN-713LC         66                                                           Waspalloy        1                                                            B-1900 + Hf     125                                                           B-1900           54                                                           Mar-M-247       195                                                           Ren- e 125      159                                                           Merl 76         217                                                           IN-100          62/67                                                         Ren- e 41        7                                                            Ren- e 80       101                                                           GMR-235          4                                                            Monalloy        200                                                           IN-792 + Hf     140                                                           SEL-15           38                                                           IN-625          103                                                           Cobalt Base - Pour Temperature 2750° F./2800° F.                X-40            122                                                           Mar-M-509        2                                                            ECY-768         178                                                           HS-31            12                                                           Mar-M-302        36                                                           Nickel-Iron - Pour Temperature 2750° F.                                IN-718C          96                                                           Hastelloy X      74                                                           ______________________________________                                    

The ceramic foam filters of the present invention are also suitable forfiltering metals having a melting point of less than 1200° C., e.g.aluminum and copper.

In accordance with the present invention, there is provided a method offiltering molten metals in general and molten superalloys in particularwhich comprises the steps of: providing a ceramic foam filter of thepresent invention; positioning the ceramic foam filter so that moltenmetal will pass through the ceramic foam filter when the metal ispoured; and pouring the molten metal through the ceramic foam filter.The positioning step may be accomplished in a number of ways.

FIG. 10 illustrates a first embodiment of the above process wherein aceramic foam filter of the present invention is positioned so thatmolten metal will pass through the ceramic foam filter an route from analloy furnace to a mold. As embodied herein, the ceramic foam filter(not visible) is placed in a tundish (5) which is positioned to receivemolten metal (6) from an alloy furnace (7). After passing through thetundish, the molten metal pours into a mold (8).

In accordance with the present invention there is provided a tundish,for use with a ceramic film filter to filter molten metal comprising amonolithic body having a bottom pour draining outlet and means forsecuring a ceramic foam filter in the path of molten metal passingthrough the tundish to the draining outlet.

FIG. 11 illustrates a first embodiment of the tundish of the presentinvention. As embodied herein, the ceramic foam filter (9) isbrick-shaped and the means for maintaining the ceramic foam filter inthe path of molten metal (not shown) passing through the tundish (10) tothe draining outlet (11) includes a pair of perforated walls (12, 13)which divide the tundish's monolithic body (14) into a molten metalreceiving chamber (15), a molten metal filtering chamber (16), and amolten metal draining chamber (17), the draining outlet being located inthe draining chamber. The filtering chamber which is located between thereceiving chamber and the draining chamber is adapted to hold thebrick-shaped ceramic foam filter between the perforated walls thatseparate the filtering chamber from the receiving chamber and thedraining chamber.

In operation molten metal received in the receiving chamber, passesthrough the perforated wall separating the receiving chamber from thefiltering chamber, then passes through the ceramic foam filter and isthereby filtered, then passes through the perforated wall separating thefiltering chamber from the draining chamber, and finally drains from thetundish through the draining outlet in the bottom of the drainingchamber.

A second embodiment of the tundish of the present invention isillustrated in FIG. 12. As embodied herein, the ceramic foam filter (18)has the shape of a cylindrical tube and the means for maintaining theceramic foam filter in the path of molten metal (not shown) passingthrough the tundish (19) to the draining outlet (20) includes aperforated wall (21) which divides the tundish's monolithic body (22)into a molten metal receiving chamber (23) and a molten metalfiltering/draining chamber (24), the draining outlet being located inthe filtering/draining chamber. The filtering/draining chamber isadapted to hold a ceramic foam filter in place directly over theinternal diameter (25) of the draining outlet. In operation, moltenmetal is received in the receiving chamber, flows through the perforatedwall separating the receiving chamber from the filering/drainingchamber, then flows through the ceramic foam filter and is therebyfiltered, and finally exits the tundish through the bottom-pour drainingoutlet.

In accordance with the present invention, FIG. 13 illustrates anotherembodiment of the method of filtering molten metal with the ceramic foamfilter of the present invention wherein the ceramic foam filter ispositioned so that molten metal will pass through the ceramic foamfilter. As embodied herein, a ceramic foam filter (26) is placed in theneck or pouring cup (27) of a mold cavity (28). Good results have beenobtained with a ceramic filter approximately 3 inches in diameter and 1inch thick. In operation, the filter may be either preheated or at roomtemperature prior to pouring the molten alloy into the mold depending onthe casting process used. The molten alloy is then poured onto andthrough the filter before entering the mold cavity. The resultingcastings are substantially free of non-metallic inclusions. FIGS. 14 and15 are photographs of actual molds with filters in their pouringcups--both before (FIG. 14) and after (FIG. 15) casting of an alloy.Different alloys, elements, and/or inclusions filter and/or reactdifferently with different ceramic filter materials, e.g., alumina,zirconia, silica, and zircon. Generally, however, castings producedusing the ceramic foam filters are of higher quality than castingsproduced without the ceramic foam filters.

Filtering molten metal with the ceramic foam filters of the presentinvention may also be accomplished by utilizing the ceramic foam filteras a bottom pour valve of a melting crucible. In accordance with thepresent invention there is provided a melting device for use in air orvacuum melting of an ingot of metal, which comprises a monolithiccrucible having a bottom pour outlet and a ceramic foam filter adaptedto be fitted into the bottom pour outlet. The length, the thickness, thediameter, the ceramic composition, and the pore size of the ceramic foamfilter valve may be selected to control the flow of metal through theceramic foam filter valve such that in operation an entire ingot ofmetal may be allowed to melt in the crucible before any metal beginspouring from the melting device.

An embodiment of the above-described melting device is illustrated inFIG. 16. As embodied therein, a ceramic metal melting crucible (29)contains an ingot of metal (30) within an induction coil (31). Embeddedin the bottom of the ceramic melting crucible is a ceramic foam filter(32). Beneath the ceramic foam filter is a casting mold (33). Themelting device works as follows: the induction power is turned on, themetal charge is heated up to its pouring temperature as quickly aspossible, the ceramic foam filter is heated by conduction from themolten metal and thereby lets molten metal pass through the filter andpour into the casting mold. Control of the passage of molten metalthrough the ceramic foam filter can be obtained by varying the length,diameter, mesh, thickness, or ceramic composition of the ceramic foamfilter valve. In this manner, the passage of the molten metal throughthe ceramic foam filter valve can be controlled such that the entireingot of metal is allowed to melt in the crucible before any of themetal begins pouring into the casting mold. This is a highly desirableachievement. In the practice of this invention ceramic foam filters havebeen varied in diameter from 1 inch to 31/2 inches and in length from3/4 inch to 21/2 inches with good results.

Preferably, passage of the metal through the ceramic foam filter valveis also controlled by supplemental heating and/or cooling of the ceramicfoam filter area. This variation is illustrated in FIG. 17. As embodiedtherein, the ceramic metal melting crucible (34) contains an ingot ofalloy (35) within an induction coil (36). A ceramic foam filter valve(37) is embedded in the bottom of the ceramic metal melting crucible. Inaddition, a heating or cooling source (38) is placed just beneath theceramic foam filter valve. The heating or cooling source is then removedwhen the melting device is ready to pour.

Another embodiment of the melting device of the present invention isillustrated in FIG. 18. As embodied herein, the neck of a casting mold(39) is produced with a melting crucible (40) containing a bottom pourceramic foam filter valve (41) in place of a pouring cup. A metal charge(42) is placed in the crucible, and an induction coil (43) is placedaround the crucible. The charge is heated as quickly as possible to thedesired pour temperature and held until the ceramic foam filter valveheats up and allows the molten metal to flow through the filter and pourinto the casting mold. FIG. 19 is another illustration of thisembodiment depicting the pouring of the molten metal through the ceramicfoam filter valve into the casting mold.

For the purpose of the present invention, the ceramic foam filters maycome in a wide variety of shapes and sizes. FIG. 20 is a photographillustrating two shapes and sizes of ceramic foam filters of the presentinvention which have worked well in the filtering of molten metal.

In accordance with the present invention there is also provided aprocess for making a ceramic porous body suitable for use with moltenmetals in general and molten superalloys in particular having a solid,high density, smooth face which comprises the steps of: providing anopen-cell, flexible, foam pattern and a face pattern the size and shapeof a face of the foam pattern to be smoothed; coating the face patternwith a ceramic slurry; stuccoing the face pattern with a coarse ceramicmaterial; impregnating the foam pattern with the ceramic slurry; placingthe impregnated foam pattern on said coated, stuccoed face pattern suchthat the impregnated foam pattern and the coated, stuccoed face patterndry together and become attached; impregnating the attached impregnatedfoam pattern and coated, stuccoed face pattern with additional ceramicslurry; removing excess dried ceramic down to the edges of foam pattern;burning out the foam pattern and the face pattern at a temperature ofbetween 1400° F. and 2200° F. to form a ceramic substrate; impregnatingthe ceramic substrate with additional ceramic slurry; and firing theimpregnated ceramic substrate at a temperature of between 2900° F. and3350° F.

An embodiment of the process for making a solid, high density, highpurity, smooth faced ceramic porous body in accordance with the presentinvention is illustrated in FIG. 21. As embodied herein, one starts witha face pattern the size and shape of the face of the ceramic articlethat is to be produced smooth and then coats the face pattern with aceramic slurry. For purposes of the present invention a wide variety ofmaterials may be used for the face pattern. Suitable materials includewax, plastic and graphite. Good results have been obtained with wax facepatterns. The coated face pattern is then stuccoed to roughen itssurface. Stuccoing may be accomplished by sprinkling a coarse ceramicmaterial onto the wet, just-coated face pattern. A wide variety ofceramic materials may be used for the stuccoing step, e.g., alumina,silica, zirconia, zircon, or magnesia. It is best to select a ceramicmaterial for stuccoing which will complement the ceramic composition ofthe ceramic slurry or slurries being used. The ceramic material forstuccoing should be coarse. Good results have been obtained with ceramicgrains in the 70-120 mesh range. The preferred stuccoing material is 100mesh alumina grain. After stuccoing the face pattern is dried. It isthen recoated and restuccoed at the same time an open-cell, flexible,foam pattern for the article to be produced is first dipped. After thefoam pattern is squeezed to remove excess slurry it is placed on thejust-coated and stuccoed face pattern. The slurry on the foam patterndries to the slurry on the face pattern causing them to become attached.From this point on the process is the same as it is for making a ceramicfoam filter except that just prior to the burn-out step excess driedceramic is removed down to the foam pattern's edge.

For purposes of the present invention, a single slurry system such asthat illustrated in FIG. 1 may be used to make the smooth faced ceramicarticle. Table 2 sets forth slurry composition and specifications for anexample of a ceramic slurry suitable for such a single slurry system.Alternatively, a ceramic slurry prewet and a ceramic slurry dipcoat maybe used as is illustrated in FIG. 4. Examples of suitable ceramic slurryprewet and dipcoat combinations are set forth in Tables 3 and 4. Specialpost-burn-out ceramic slurries differing from the slurries used in thepre-burn-out steps may also be employed in making the smooth facedceramic porous body of the present invention. Examples of suchpost-burn-out ceramic slurries are set forth in Tables 7 and 8.

There are many possible applications for the smooth faced ceramic porousbodies of the present invention. FIG. 22 is a photograph of a ceramicfoam brick with a high density, high purity, smooth face. This articleis suitable for use an insulating refractory lining for, inter alia,furnaces, kilns, or ladles. FIG. 23 illustrates the use of such a highdensity, high purity, smooth faced ceramic porous body (43) as aninsulating refractory lining for a ladle (44).

The method for making a smooth faced ceramic body of the presentinvention may also be used to produce ceramic foam melting crucibles.FIG. 24 is a photograph of a ceramic foam melting crucible made inaccordance with the present invention. FIG. 25 illustrates anotherembodiment of the ceramic foam melting crucible (45) of the presentinvention.

The process of the present invention can also be used to make ceramiccores having a solid, high density, high purity, smooth exterior face.FIG. 26 illustrates an example of such a ceramic core (46).

As with the ceramic foam filters of the present invention, all of thesesmooth faced ceramic foam objects are suitable for use with molten metalin general and molten superalloys in particular.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided that they come within the scope ofthe appended claims and their equivalents.

What is claimed is:
 1. A process for making a ceramic foam filtersuitable for use in filtering molten metals in general and moltensuperalloys in particular which comprises the steps of: providing anopen-cell, flexible foam pattern; impregnating said foam pattern with aceramic slurry; burning out said foam pattern at a temperature ofbetween 1400° F. and 2200° F. to form a ceramic substrate; impregnatingsaid ceramic substrate with additional ceramic slurry; and firing saidimpregnated ceramic substrate at a temperature of between 2200° F. and3400° F.
 2. The process of claim 1 wherein the temperature at which saidpolyurethane foam pattern is burned out is about 1800° F.
 3. The processof claim 1 wherein the temperature at which said impregnated ceramicsubstrate is fired is about 3100° F.
 4. The process of claim 1 whereinsaid open-cell, flexible foam pattern is a polyurethane foam.
 5. Theprocess of claim 1 wherein said polyurethane foam is a reticulated,fully open-pore, flexible, ester type, polyurethane foam having between10 and 30 pores per inch.
 6. The process of claim 1 wherein the step ofimpregnating said foam pattern with a ceramic slurry includes the stepsof dipping said foam pattern into a ceramic slurry dipcoat, drainingexcess slurry from said pattern, drying said foam pattern, redippingsaid foam pattern into said ceramic slurry dipcoat, draining excessslurry from said foam pattern without squeezing, and drying said foampattern; and the step of impregnating said ceramic substrate withadditional ceramic slurry includes the steps of dipping said ceramicsubstrate into said ceramic slurry dipcoat, draining excess slurry fromsaid ceramic substrate, and drying said ceramic substrate.
 7. Theprocess of claim 6 wherein said redipping, draining and drying of saidfoam pattern is repeated at least once.
 8. The process of claim 6wherein said ceramic slurry dipcoat has a composition of between 1% and20% silica by weight (dry basis) and between 99% and 80% alumina byweight (dry basis), a viscosity of between 5 and 20 seconds, and a filmweight of between 1.0 and 8.0 grams per standard six inch square plate.9. The process of claim 8 wherein said ceramic slurry dipcoat comprisesabout 9.2% silica by weight (dry basis) and about 90.8% alumina byweight (dry basis), has a viscosity of between 10 and 13 seconds, and afilm weight of between 3.7 and 4.0 grams per standard six inch squareplate.
 10. The process of claim 8 wherein said silica is aqueouscolloidal silica and said alumina is -325 mesh alumina flour.
 11. Theprocess of claim 8 wherein said ceramic slurry dipcoat composition alsoincludes a suspending agent, a wetting agent and a defoaming agent. 12.The process of claim 11 wherein said suspending agent is polyvinylchloride latex, said wetting agent is an organic phosphate ester, andsaid defoaming agent is ethylhexanol.
 13. The process of claim 1 whereinthe step of impregnating said foam pattern with a ceramic slurryincludes the step of dipping said foam pattern into a ceramic slurryprewet and a ceramic slurry dipcoat, and the step of impregnating saidceramic substrate with additional ceramic slurry includes the step ofdipping said ceramic substrate into said ceramic slurry prewet.
 14. Theprocess of claim 13 wherein said step of dipping said foam pattern intoa ceramic slurry prewet and a ceramic slurry dipcoat includes the stepsof dipping said foam pattern into said ceramic slurry prewet, drainingexcess slurry from said foam pattern, dipping said foam pattern intosaid ceramic slurry dipcoat, draining excess slurry from said foampattern, drying said foam pattern, redipping said foam pattern into saidceramic slurry prewet, draining excess slurry from said foam patternwithout squeezing, redipping said foam pattern into said ceramic slurrydipcoat, draining excess slurry from said foam pattern without squeezingand drying said foam pattern, said redipping into prewet, draining,redipping into dipcoat, draining and drying steps being repeated atleast once.
 15. The process of claim 13 wherein said ceramic slurrydipcoat has a composition of between 1% and 20% silica by weight (drybasis) and between 99% and 80% alumina by weight (dry basis), aviscosity of between 5 and 60 seconds, and a film weight of between 1.0and 8.0 grams per standard six inch square plate, and said ceramicslurry prewet has a composition of between 1% and 30% silica by weight(dry basis) and between 99% and 70% alumina by weight (dry basis), and aviscosity of between 1 and 25 seconds.
 16. The process of claim 15wherein said ceramic slurry dipcoat comprises about 9.2% silica byweight (dry basis) and about 90.8% alumina by weight (dry basis), has aviscosity of between 24 and 30 seconds, and a film weight of between 4.5and 5.5 grams per standard six inch square plate, and said ceramicslurry prewet comprises about 11.9% silica by weight (dry basis) andabout 88.1% alumina by weight (dry basis), and has a viscosity ofbetween 8 and 10 seconds.
 17. The process of claim 15 wherein saidsilica is aqueous colloidal silica and said alumina is -325 mesh aluminaflour.
 18. The process of claim 15 wherein said ceramic slurry dipcoatand said ceramic slurry prewet also include a suspending agent, awetting agent and a defoaming agent.
 19. The process of claim 18 whereinsaid suspending agent is polyvinyl chloride latex, said wetting agent isan organic phosphate ester, and said defoaming agent is ethylhexanol.20. The process of claim 13 wherein said ceramic slurry dipcoat has acomposition of between 1% and 20% colloidal silica solids by weight (drybasis) and between 99% and 80% fused silica solids by weight (drybasis), a viscosity of between 10 and 80 seconds, and a film weight ofbetween 1 and 14 grams per standard six inch square plate, and saidceramic slurry preset has a composition of between 1% and 30% colloidalsilica solids by weight (dry basis) and between 99% and 70% fused silicasolids by weight (dry basis), and a viscosity of between 1 and 25seconds.
 21. The process of claim 20 wherein said ceramic slurry dipcoatcomprises about 12.4% colloidal silica solids by weight (dry basis) andabout 87.6% fused silica solids by weight (dry basis), has a viscosityof between 40 and 50 seconds, and a film weight of between 5 and 7 gramsper standard six inch square plate, and said ceramic slurry prewetcomprises about 24.8% colloidal silica solids by weight (dry basis) andabout 75.2% fused silica solids by weight (dry basis), and has aviscosity of between 6 and 8 seconds.
 22. The process of claim 20wherein said fused silica solid is -325 mesh silica flour.
 23. Theprocess of claim 20 wherein said ceramic slurry dipcoat composition andsaid ceramic slurry prewet composition also include a suspending agent,a wetting agent and a defoaming agent.
 24. The process of claim 23wherein said suspending agent is polyvinyl chloride latex, said wettingagent is an organic phosphate ester, and said defoaming agent isethylhexanol.
 25. The process of claim 1 wherein the step ofimpregnating said ceramic substrate with additional ceramic slurryincludes the steps of dipping said ceramic slurry into a post-burnoutceramic slurry dipcoat, draining excess slurry from said ceramicsubstrate, and drying said ceramic substrate, said post-burnout ceramicslurry dipcoat comprising zirconia and having a viscosity of between 1and 20 seconds.
 26. The process of claim 25 wherein said viscosity isabout 5 seconds.
 27. The process of claim 25 wherein said zirconia is-325 mesh zirconia.
 28. The process of claim 25 wherein saidpost-burnout ceramic slurry dipcoat also includes a polyelectrolytedispersing agent and a suspending agent.
 29. The process of claim 28wherein said suspending agent is citric acid.
 30. The process of claim 1wherein the step of impregnating said ceramic substrate with additionalceramic slurry includes the steps of dipping said ceramic slurry into apost-burnout ceramic slurry dipcoat, draining excess slurry from saidceramic substrate, and drying said ceramic substrate, said post-burnoutceramic slurry dipcoat comprising alumina and having a viscosity ofbetween 1 and 20 seconds.
 31. The process of claim 31 wherein saidviscosity is about 7 seconds.
 32. The process of claim 30 wherein saidalumina has an ultimate crystal size of between 3.0 and 3.5 μm and analumina content of greater than 99.5%.
 33. The process of claim 30wherein said post-burnout ceramic slurry dipcoat also includes apolyelectrolyte dispersing agent and a suspending agent.
 34. The processof claim 33 wherein said suspending agent is citric acid.
 35. A ceramicfoam filter useful as a filtering material for molten metal in generaland molten superalloys in particular made by the process of claim
 1. 36.A ceramic foam filter useful as a filtering material for molten metal ingeneral and molten superalloys in particular made by the process ofclaim
 8. 37. A ceramic foam filter useful as a filtering material formolten metal in general and molten superalloys in particular made by theprocess of claim
 15. 38. A ceramic foam filter useful as a filteringmaterial for molten metal in general and molten superalloys inparticular made by the process of claim
 20. 39. A ceramic foam filteruseful as a filtering material for molten metal in general and moltensuperalloys in particular made by the process of claim
 25. 40. A ceramicfoam filter useful as a filtering material for molten metal in generaland molten superalloys in particular made by the process of claim 30.41. A process for making a ceramic porous body suitable for use withmolten metals in general and molten superalloys in particular having asolid, high density, high purity, smooth face which comprises the stepsof: providing an open-cell, flexible, foam pattern and a face patternthe size of a face of said foam pattern to be smoothed; coating saidface pattern with a ceramic slurry; stuccoing said face pattern with acoarse ceramic material; impregnating said foam pattern with saidceramic slurry; placing said impregnated foam pattern on said coated,stuccoed face pattern such that said impregnated foam pattern and saidcoated, stuccoed face pattern dry together and become attached;impregnating said attached impregnated foam pattern and coated, stuccoedface pattern with additional ceramic slurry; removing excess driedceramic down to the edges of said foam pattern; burning out said foampattern and said face pattern at a temperature of between 1400° F. and2200° F. to form a ceramic substrate; impregnating said ceramicsubstrate with additional ceramic slurry; and firing said impregnatedceramic substrate at a temperature of between 2200° F. and 3400° F. 42.The process of claim 41 wherein the step of impregnating said attachedimpregnated foam pattern and coated stuccoed face pattern withadditional ceramic slurry includes the steps of dipping said attachedfoam pattern and face pattern into a ceramic slurry dipcoat, drainingexcess slurry from said attached foam pattern and face pattern, dryingsaid attached foam pattern and face pattern, redipping said attachedfoam pattern and face pattern into said ceramic slurry dipcoat, drainingexcess slurry from said attached foam pattern and face pattern withoutsqueezing, and drying said attached foam pattern and face pattern; andthe step of impregnating said ceramic substrate with additional ceramicslurry includes the steps of dipping said ceramic substrate into saidceramic slurry dipcoat, draining excess slurry from said ceramicsubstrate, and drying said ceramic substrate.
 43. The method of claim 41wherein said ceramic slurry dipcoat has a composition of between 1% and20% silica by weight (dry basis) and between 99% and 80% alumina byweight (dry basis), a viscosity of between 5 and 20 seconds, and a filmweight of between 1.0 and 8.0 grams per standard six inch square plate.44. The method of claim 41 wherein the step of impregnating saidattached impregnated foam pattern and coated, stuccoed face pattern withadditional ceramic slurry includes the step of dipping said attachedfoam pattern and face pattern into a ceramic slurry prewet and a ceramicslurry dipcoat, and the step of impregnating said ceramic substrate withadditional ceramic slurry includes the step of dipping said ceramicsubstrate into said ceramic slurry prewet.
 45. The method of claim 44wherein said ceramic slurry dipcoat has a composition of between 1% and20% silica by weight (dry basis) and between 99% and 80% alumina byweight (dry basis), a viscosity of between 5 and 60 seconds, and a filmweight of between 1.0 and 8.0 grams per standard six inch square plate,and said ceramic slurry prewet has a composition of between 1% and 30%silica by weight (dry basis) and between 99% and 70% alumina by weight(dry basis), and a viscosity of between 1 and 25 seconds.
 46. The methodof claim 44 wherein said ceramic slurry dipcoat has a composition ofbetween 1% and 20% colloidal silica solids by weight (dry basis) andbetween 99% and 80% fused silica solids by weight (dry basis), aviscosity of between 10 and 80 seconds, and a film weight of between 1and 14 grams per standard six inch square plate, and said ceramic slurryprewet has a composition of between 1% and 30% colloidal silica solidsby weight (dry basis) and between 99% and 70% fused silica solids byweight (dry basis), and a viscosity of between 1 and 25 seconds.
 47. Theprocess of claim 41 wherein the step of impregnating said ceramicsubstrate with additional ceramic slurry includes the steps of dippingsaid ceramic slurry into a post-bur-out ceramic slurry dipcoat, drainingexcess slurry from said ceramic substrate, and drying said ceramicsubstrate, said post-burn-out ceramic slurry dipcoat comprising zirconiaand having a viscosity of between 1 and 20 seconds.
 48. The process ofclaim 41 wherein the step of impregnating said ceramic substrate withadditional ceramic slurry includes the steps of dipping said ceramicslurry into a post-burn-out ceramic slurry dipcoat, draining excessslurry from said ceramic substrate, and drying said ceramic substrate,said post-burn-out ceramic slurry dipcoat comprising alumina and havinga viscosity of between 1 and 20 seconds.
 49. Insulating refractorylining for large metal melting furnaces and ladles suitable for use withmolten metal in general and molten superalloys in particular comprisingceramic porous bodies made by the process of claim
 41. 50. Insulatingrefractory lining for large metal melting furnaces and ladles suitablefor use with molten metals in general and molten superalloys inparticular comprising ceramic porous bodies made by the process of claim43.
 51. Insulating refractory lining for large metal melting furnacesand ladles suitable for use with molten metals in general and moltensuperalloys in particular comprising ceramic porous bodies made by theprocess of claim
 45. 52. Insulating refractory lining for large metalmelting furnaces and ladles suitable for use with molten metals ingeneral and molten superalloys in particular comprising ceramic porousbodies made by the process of claim
 46. 53. Insulating refractory liningfor large metal melting furnaces and ladles suitable for use with moltenmetals in general and molten superalloys in particular comprisingceramic porous bodies made by the process of claim
 47. 54. Insulatingrefractory lining for large metal melting furnaces and ladles suitablefor use with molten metals in general and molten superalloys inparticular comprising ceramic porous bodies made by the process of claim48.
 55. A melting crucible suitable for use with molten metals ingeneral and molten superalloys in particular and having a solid, highdensity, high purity, smooth, internal face, comprising a ceramic porousbody made from the method of claim
 41. 56. A melting crucible suitablefor use with molten metals in general and molten superalloys inparticular and having a solid, high density, high purity, smooth,internal face, comprising a ceramic porous body made from the method ofclaim
 43. 57. A melting crucible suitable for use with molten metals ingeneral and molten superalloys in particular and having a solid, highdensity, high purity, smooth, internal face, comprising a ceramic porousbody made from the method of claim
 45. 58. A melting crucible suitablefor use with molten metals in general and molten superalloys inparticular and having a solid, high density, high purity, smooth,internal face, comprising a ceramic porous body made from the method ofclaim
 46. 59. A melting crucible suitable for use with molten metals ingeneral and molten superalloys in particular and having a solid, highdensity, high purity, smooth, internal face, comprising a ceramic porousbody made from the method of claim
 47. 60. A melting crucible suitablefor use with molten metals in general and molten superalloys inparticular and having a solid, high density, high purity, smooth,internal face, comprising a ceramic porous body made from the method ofclaim
 48. 61. A ceramic core suitable for use with molten metals ingeneral and molten superalloys in particular and having a solid, highdensity, high purity, smooth, exterior face, comprising a ceramic bodymade from the process of claim
 41. 62. A ceramic core suitable for usewith molten metals in general and molten superalloys in particular andhaving a solid, high density, high purity, smooth, exterior face,comprising a ceramic body made from the process of claim
 43. 63. Aceramic core suitable for use with molten metals in general and moltensuperalloys in particular and having a solid, high density, high purity,smooth, exterior face, comprising a ceramic body made from the processof claim
 45. 64. A ceramic core suitable for use with molten metals ingeneral and molten superalloys in particular and having a solid, highdensity, high purity, smooth, exterior face, comprising a ceramic bodymade from the process of claim
 46. 65. A ceramic core suitable for usewith molten metals in general and molten superalloys in particular andhaving a solid, high density, high purity, smooth, exterior face,comprising a ceramic body made from the process of claim
 47. 66. Aceramic core suitable for use with molten metals in general and moltensuperalloys in particular and having a solid, high density, highpurrity, smooth, exterior face, comprising a ceramic body made from theprocess of claim 48.